Typically, polysilicon is used for gate electrodes and patterned using a multiple step process. In the multiple step process, a first anisotropic etch step quickly removes a first portion of the polysilicon. Next, an etch that is selective to the underlying dielectric layer removes a second portion of the polysilicon. This etch results in a tapered sidewall profile for the second portion of the polysilicon. To remove the tapering and silicon stringers left on the wafer, a third etch is performed. Some gases typically used are HBr, CF4, Cl2, He/O2, and O2.
As the semiconductor industry moves to high-performance devices, polysilicon depletion becomes a problem and needs to be minimized or eliminated. One way to address this need is to use a metal control electrode. However, the chemistries used for polysilicon do not work well for etching metal control electrodes while stopping on any underlying gate dielectric layer. Therefore, a need exists for a process for etching metal control electrodes, especially metal control electrodes over metal oxides.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to, other elements to help improve the understanding of the embodiments of the present invention.